If anything, the president has grown even more defiant since Mr. Mueller found insufficient evidence to establish a criminal conspiracy between the Trump campaign and Russia, almost as if having avoided charges, he is daring the establishment to come after him again. The man who once said he could shoot someone on Fifth Avenue in Manhattan without consequence seems to be testing whether he can do the political equivalent.

“What he’s learned is you can get away with just about anything if you’re willing to gamble and you have zero shame,” said Gwenda Blair, a biographer of the Trump family. “He had just outbluffed the old-school way of holding people to account, so what the heck, why not go for it in the phone call to the new, young and vulnerable Ukrainian president?”…

Some critics said it did not even matter if Mr. Trump explicitly linked the two issues in the call; simply using the power and prestige of his office to lean on a foreign leader for help in a domestic political contest by itself could justify impeachment, they said. And suspending the aid, they said, appeared to be a corrupt exercise of presidential power to benefit himself, whether he mentioned it to Mr. Zelensky or not.

But Mr. Trump’s defenders said he was being targeted for partisan and political reasons, his every move interpreted in the most cynical light and distorted to tarnish his reputation, while adversaries like Mr. Biden are given a free pass.